U.S. patent number 4,961,310 [Application Number 07/374,812] was granted by the patent office on 1990-10-09 for single shaft combined cycle turbine.
This patent grant is currently assigned to General Electric Company. Invention is credited to James H. Moore, Klaus M. Retzlaff, Kenneth E. Robbins.
United States Patent |
4,961,310 |
Moore , et al. |
October 9, 1990 |
Single shaft combined cycle turbine
Abstract
An improved combined cycle plant with a gas turbine, a steam
turbine and a generator arranged in tandem on a single shaft system
in the order aforementioned, including a single thrust bearing with
rigidly coupled rotor members. A thrust bearing for the shaft
system is supported in a bearing standard keyed to the foundation
on the side of the steam turbine toward the gas turbine to restrain
axial movement. The thrust bearing is preferably located in the
compressor inlet of the gas turbine. The steam turbine comprises a
first casing with the hihg pressure section supported in a bearing
standard keyed to the foundation adjacent the thrust bearing. The
second casing with the low pressure section is keyed to the
foundation at its outlet in the center of the exhaust hood. In a
preferred arrangement with a single flow low pressure turbine
section, the second casing combines an intermediate pressure
turbine section adjacent the generator receiving steam from the
reheater. In a modified arrangement with a double flow low pressure
section, the intermediate pressure turbine section turbine section
is combined with the high pressure turbine section in the first
casing.
Inventors: |
Moore; James H. (Schenectady,
NY), Retzlaff; Klaus M. (Schenectady, NY), Robbins;
Kenneth E. (Saratoga, NY) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
23478286 |
Appl.
No.: |
07/374,812 |
Filed: |
July 3, 1989 |
Current U.S.
Class: |
60/39.182;
415/213.1; 60/796 |
Current CPC
Class: |
F01D
25/28 (20130101); F01D 25/168 (20130101); F01D
25/162 (20130101); F01K 23/16 (20130101); Y02E
20/16 (20130101) |
Current International
Class: |
F01K
23/00 (20060101); F01D 25/16 (20060101); F01K
23/16 (20060101); F01D 25/28 (20060101); F02C
007/20 () |
Field of
Search: |
;60/39.182,39.31,39.32
;415/134,213.1,220 ;248/605,606,639,901 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Casaregola; Louis J.
Attorney, Agent or Firm: Nixon & Vanderhye
Claims
I claim:
1. In a combined cycle plant having a gas turbine, a steam turbine,
and a generator all being disposed on a foundation and arranged in
tandem in the order aforementioned on a single shaft system having
a single thrust bearing and a plurality of rigidly coupled rotor
members, the improvement comprising:
said thrust bearing being supported on first means keyed to said
foundation on the side of said steam turbine toward said gas
turbine to restrain axial movement of said single shaft system,
said steam turbine comprising a reheat steam turbine having a first
casing supported at one end thereof on second means keyed to said
foundation adjacent said thrust bearing to be restrained against
axial movement,
said reheat turbine having an exhaust hood and having a second
casing supported at least in part within said exhaust hood, said
second casing being supported on third means keyed to said
foundation near the center of the exhaust hood outlet, whereby said
first and second casings grow thermally independently of one
another and independently of said single shaft system.
2. The improvement accordingly to claim 1, and further including a
high pressure turbine section disposed in said first casing, an
intermediate pressure section connected to receive steam reheated
by the exhaust from said gas turbine, and a low pressure turbine
section disposed in said second casing connected to receive steam
from said intermediate pressure section and discharging into said
exhaust hood.
3. The improvement according to claim 2, further including a
bearing standard disposed on the end of said second casing toward
said generator, said second casing being mounted on said bearing
standard to allow axial movement with respect to said third means,
said intermediate pressure turbine section being disposed in said
second casing, and said low pressure turbine section being a single
flow turbine.
4. The improvement according to claim 3, wherein said high pressure
turbine section employs interlocking high-low packings to provide
for greater thermal efficiency and wherein said intermediate
pressure turbine section employs non-interlocking packings
permitting substantial relative movement between rotating and
non-rotating members in order to accommodate substantial
differential thermal expansion.
5. The improvement according to claim 2, wherein said first casing
has an inlet end and is disposed with said inlet end located
nearest said thrust bearing, wherein said intermediate pressure and
low pressure turbine sections are disposed in said second casing
combined with an exhaust hood, said second casing having an inlet
end disposed on the side of the steam turbine toward said
generator, whereby said second casing grows toward the inlet end
thereof independently of said first casing.
6. The improvement according to claim 2, wherein said high pressure
turbine section and intermediate pressure turbine section are
combined in said first casing, and wherein said low pressure
turbine section comprises a double-flow turbine in said second
casing, said exhaust hood being keyed to said foundation at its
center to restrain axial movement, whereby said second casing grows
thermally independently of said first casing.
7. The improvement according to claim 1, wherein the first casing
is supported at its other end on a first bearing standard adapted
to permit axial movement of said other end with respect to the
foundation.
8. The improvement according to claim 1, wherein said second casing
is partially supported at one end thereof on a second bearing
standard adapted to permit axial movement with respect to the
foundation.
9. The improvement according to claim 1, wherein said first and
second casings are each partially supported on a common bearing
standard disposed between them, said common bearing standard being
arranged to move axially with respect to the foundation and one of
said casings being adapted to move axially with respect to said
common bearing standard.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to large combined cycle power
systems having a steam turbine and gas turbine, together driving an
electrical generator as the load, and more particularly to
improvements in a tandem arrangement of gas turbine, steam turbine
and generator on a single shaft system of rigidly coupled rotor
members and having a single thrust bearing for the rotor
system.
Many arrangements for gas turbines and steam turbines in a combined
cycle have been proposed. A combined cycle is an integrated thermal
cycle, wherein the hot exhaust gas from a combustion gas turbine
contributes heat energy to partially or wholly generate the steam
used in the steam turbine. Combined cycle power plants have been
built with the gas turbine, steam turbine and generator rotors
connected in tandem by flexible or by solidly bolted rigid
couplings. If the rotor members in the single shaft system are
rigidly coupled, only one thrust bearing can be employed, since the
shaft system expands or grows in an axial direction due to thermal
expansion from the thrust bearing.
A proposal for a single shaft combined cycle having gas turbine,
single-flow non-reheat steam turbine and generator connected in
tandem in the order aforesaid on a single shaft system with rigidly
coupled rotor members and a single thrust bearing is disclosed in
Japanese patent publication No. 62-38525, published May 6, 1983. In
this publication, the single thrust bearing is located between the
gas turbine and the steam turbine. The single-flow steam turbine
section is arranged in flow opposition to the gas turbine in order
to create thrust in opposition to that of the gas turbine, and
thereby reduce the size of the thrust bearing. However, no
provisions are shown for support of the members on the foundation
or to provide for thermal expansion.
Gas turbines have now been developed that have substantially higher
power ratings and higher exhaust temperatures than previously
available. Because of this, higher rated steam turbines are
required and a reheat steam cycle is economically attractive for
combined cycle applications. A conventional reheat steam turbine
requires at least two casings which are normally arranged to reduce
the unbalanced thrust. A typical arrangement for a two-casing
reheat turbine having a single flowed low pressure section has
three bearing standards, the center bearing standard supporting one
end of each of the casings and also containing a thrust bearing.
The two casings are keyed to the foundation at only one point,
preferably the center of the exhaust hood connection in the low
pressure section. The center bearing standard with the thrust
bearing is arranged to move relative to the foundation. The two
casings supported by the center bearing standard are also keyed to
it so that the casings move together with the bearing standard,
while the shaft and both casings grow thermally in opposite
directions from one another relative to the center bearing
standard. While this is an ideal arrangement for a reheat steam
turbine, it is not possible to simply substitute a conventional two
casing reheat steam turbine design into a single shaft combined
cycle of the type described above, since a two casing reheat steam
turbine has a moving thrust bearing between the casings. Keying of
the thrust bearing to the foundation on either outside end of the
two casings or keying the center thrust bearing standard to the
foundation between the casings is not normally considered because
this would create large differential thermal expansion between
rotating and non-rotating members and result in unacceptable
efficiency losses.
Accordingly, one object of the present invention is to provide an
improved combined cycle plant having a gas turbine, as steam
turbine and a generator arranged in tandem in the order aforesaid
on a single shaft system with a single thrust bearing, while
attaining the high efficiency of a conventional steam turbine
design.
A further object of the invention is to provide an improved reheat
steam turbine foundation support and anchor point arrangement which
is especially adapted for such a single shaft combined cycle
plant.
SUMMARY OF THE INVENTION
Briefly stated, the invention comprises an improved combined cycle
plant having a gas turbine, a steam turbine and a generator
arranged in tandem on a single shaft system including a single
thrust bearing with rigidly coupled rotor members, wherein the
improvement comprises a thrust bearing for the shaft system
supported on first means keyed to the foundation on the side of the
steam turbine toward the gas turbine to restrain axial movement of
the shaft system, and wherein the steam turbine comprises a
two-casing reheat steam turbine having a high pressure turbine
section, an intermediate pressure turbine section receiving steam
which has been reheated by the gas turbine exhaust, and a low
pressure turbine section discharging into an exhaust hood. The
first casing is supported at one end on second means keyed to the
foundation adjacent the thrust bearing, while the other end is
allowed to move. The second casing is supported at least in part
within the exhaust hood on third means keyed to the foundation at
the center of the exhaust hood. In a preferred form of the
invention the intermediate pressure section is disposed in the
second casing and supported on a standard near the generator to
allow axial movement thereof. A modified form of the invention
combines high pressure and intermediate pressure turbine sections
in the first casing and uses double-flow low pressure sections
completely within the exhaust hood as the second casing.
The disclosed arrangements of the casings provide for opposed flow
in the turbine sections to minimize thrust load, minimize
differential expansion between stationary and moving blades and
achieve smallest clearances between nozzles and buckets in the hot
operating condition for best efficiency. Further improvements
include employment of stepped high-low packings for efficiency and
single diameter packings permitting substantial relative movement
at the appropriate places in both embodiments.
DRAWING
The subject matter which is regarded as the invention is
particularly pointed out and distinctly claimed in the concluding
portions of the specification. The invention, however, both as to
organization and method of practice, together with further objects
and advantages thereof, may best be understood by reference to the
following description, taken in connection with the accompanying
drawing in which:
FIG. 1 is a simplified schematic drawing of a prior art reheat
steam turbine with a single flow low pressure section;
FIG. 2 is a simplified schematic drawing of a combined cycle power
plant in accordance with the present invention;
FIG. 3 is a more detailed schematic side elevational view of the
improved reheat steam turbine arrangement according to the present
invention;
FIG. 4 is a fragmentary side elevational view of a portion of a
typical steam turbine stage in the high pressure turbine
section;
FIG. 5 is a fragmentary side elevational view, partly in section,
of a typical turbine stage in the lower pressure turbine
section;
FIG. 6 is a simplified schematic drawing of a prior art reheat
steam turbine with a double flow low pressure section,
FIG. 7 is a simplified schematic drawing of a combined cycle
according to a modified form of the invention,
FIG. 8 is a more detailed schematic side elevational drawing of the
reheat steam turbine shown in the FIG. 7 modification, and
FIG. 9 is a partial schematic side elevational view illustrating an
alternate bearing standard for the FIG. 8 modification.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring now to FIG. 1 of the drawing, a prior art reheat steam
turbine is shown which includes a single-flow high pressure turbine
section in a first casing 2 and a single-flow turbine in a second
casing 4 receiving reheat steam. The turbine casing 4 comprises an
intermediate pressure turbine section, and a low pressure turbine
section emptying into an exhaust hood. The casings 2, 4 are
disposed on either side of and supported at their inlet ends by
pairs of supporting arms keyed at 3 and 5 respectively to a central
bearing standard 6. Central standard 6 also incorporates a central
thrust bearing 8 and a journal bearing 9. Bearing standard 6 may
move axially by sliding on a foundation baseplate 7 as indicated by
the arrow 29. Turbine sections in casings 2, 4 are arranged in
opposed flow relationship in order to minimize thrust carried by
the thrust bearing 8. A front bearing standard 10 is supported by
the foundation 11 on flexible legs 12 and supports a high pressure
shaft journal bearing 15 and the high pressure casing outlet end on
pairs of support arms which are keyed to the standard 10 at
reference number 13. A rear bearing standard 14 supports the low
pressure casing and rotor journal bearing 19. Beyond the bearing
standard 14, the rotor is connected by coupling 20 to a generator
(not shown). The low pressure exhaust hood is keyed at 16 to the
foundation 17, near the center of its outlet where the exhaust hood
connects to a condenser through an expansion joint. Preventing
movement at this point avoids imposing shear loading on the
expansion joint. Since both casings are keyed to the slidable
central standard 6, the casings both grow thermally to the left
from keyed point 16. The two rotor members for the respective
turbine sections are rigidly coupled together by a coupling 18, and
expand thermally in both directions from thrust bearing 8.
Therefore, relative to the central bearing standard 6, the inlet
ends of both casings are least subject to differential expansion
between rotating and stationary components.
While the prior art arrangement of FIG. 1 is suitable for a reheat
steam turbine power plant in a multi-shaft combined cycle, it is
not suitable for a single shaft, combined cycle plant with a gas
turbine on a single shaft system having a single thrust bearing,
since the thrust bearing 8 and the central standard 6 move axially
and this would cause unacceptable axial movement of the gas turbine
rotor in its casing.
Reference to FIG. 2 of the drawing illustrates a simplified
schematic drawing of a single shaft combined cycle plant utilizing
an improved reheat steam turbine single flow arrangement in
accordance with a preferred embodiment of the present invention.
There, a gas turbine shown generally at 21 and a steam turbine
shown generally at 22, are arranged in tandem with a generator 24
in the order aforementioned on a rigidly coupled single shaft
system having a single thrust bearing 26. Thrust bearing 26 is
supported in a bearing standard 27 in the gas turbine compressor
inlet comprising first means supporting the thrust bearing 26 and
keyed to the foundation at 28 directly below thrust bearing 26 to
restrain axial movement of the single shaft system at this point.
The single shaft system is shown generally as 30, and runs through
the gas turbine 21, steam turbine 22 and generator 24, comprising
rigidly coupled rotor members.
The gas turbine 21 includes a compressor 32, fuel combustor 33 and
turbine 34 on a bed plate 35. The turbine exhaust end is supported
on the bedplate 35 on flexible legs 36 permitting axial movement of
compressor and turbine from front standard 27, while the shaft
expands toward the left, when heated, from thrust bearing 26.
Turbine 34 exhausts hot gas through a heat recovery steam generator
38. The heat recovery steam generator 38 may be either fired or
unfired and may generate steam at several pressure levels, but is
shown in its simplest form as including at least a primary high
pressure steam generator 40 and a steam reheater 42. The steam
turbine 22 includes a high pressure turbine section 44 in a first
casing 92 connected to receive steam through valves from the
primary steam generator 40 at its inlet end, exhausting steam to
reheater 42. A turbine shown generally at 45 which consists of a
combined intermediate pressure turbine section 46 and single flow
low pressure turbine section 48 combined in a single second casing
98 is connected to receive steam at its inlet end from reheater 42
and to exhaust it through an exhaust hood 49 (see FIG. 3) to
condenser 50.
The single shaft system shown generally at 30 consists of a number
of rotor members rigidly connected together by rigid couplings such
as 54 and supported in journal bearings such as 56. The casing 98
of turbine 45 is supported at one end in the exhaust hood 49 which,
in turn, is supported partially by bearing standard 57 and keyed to
the foundation at 58. The exhaust hood also rests on the foundation
at several locations which are not seen in the plane of the
drawing. Axial movement of the casing 98 inlet end is permitted by
flexible legs on bearing standard 76, as shown by arrows 79.
The high pressure turbine section 92 has the inlet of its casing 92
supported on a front bearing standard 60 on arms keyed to the
standard at 61. The outlet end of the casing 92 may slide on arms
supported on standard 57 as shown by arrows 80. Standard 60 is
keyed to the foundation at 62 to restrain it against axial
movement.
Referring now to FIG. 3 of the drawing, a more detailed schematic
view of the improved reheat steam turbine arrangement is shown,
with the single shaft system 30 shown as a single line. The
two-casing reheat steam turbine 22 is supported on a foundation,
portions of which are indicated at 64, 68, 70. The front bearing
standard 60 is supported on the foundation 64 and keyed to it at 62
on the side of the steam turbine toward the thrust bearing 26 to
restrain against axial movement. Standard 60 also supports a
turning gear 72 and a journal bearing 74.
The rear bearing standard 76 at the opposite end of the steam
turbine on the side toward the generator is supported on foundation
member 70 on flexible legs 77 as shown, or alternatively on a
sliding standard, permitting axial movement (arrows 79) and
includes a journal bearing 78. The central standard 57 is supported
on foundation member 68 between turbines 44 and 45 and includes a
journal bearing 82. As previously mentioned, turbine 45 combines an
intermediate pressure turbine section 46 and a low pressure turbine
section 48 in a second casing 98, supported at one end in exhaust
hood 49 which is also considered part of the second casing. The
outlet from the exhaust hood 49 is keyed at 58 to the foundation at
the connection to a condenser expansion joint (not shown), and also
partially supported on the foundation.
Portions of the single shaft system 30 which are shown in FIG. 3
are a high pressure steam turbine rotor member 84 and a low
pressure turbine rotor member 83 rigidly coupled together at 88.
These two rotor members are supported in three journal bearings 74,
82, 78. Rotor member 84 is rigidly coupled to the gas turbine
through a spacer or spool piece 85 by rigid couplings 86, 87. Rotor
member 83 is rigidly coupled to the generator by rigid coupling
54.
The turbine 44, includes a first casing 92 supported at one end by
a pair of arms 93 keyed to standard 60 at 61 with an inlet end 94
nearest the thrust bearing 26. Since the standard 60 is keyed to
the foundation at 62, it serves as second means supporting the
first casing keyed to the foundation adjacent the thrust bearing.
Casing 92 is supported at its other end on an opposite pair of arms
95 slidable on standard 57 at the casing outlet end 96 (arrows
80).
The second casing 98 is separately keyed to the foundation at 58.
Standard 57 is rigidly connected to low pressure turbine section
48, and is slidable on foundation 68. The exhaust hood 49 is
supported by standard 57 and by the foundation itself. Exhaust hood
49 and standard 57 together comprise third means supporting the
second casing keyed to the foundation near the center of the
exhaust hood outlet.
Casing 98 is supported on a pair of arms 99 at its inlet end 100
keyed to the rear bearing standard 76 at 101. Flexible legs 77
permit deflection of the standard 76 axially as shown by arrows 79.
Alternatively, the rear standard 76 could slide on the
foundation.
Referring to FIGS. 4 and 5 of the drawing, typical single turbine
stages are shown from the high pressure turbine 44 in the first
casing and the intermediate pressure turbine 45 in the second
casing, respectively. FIGS. 4 and 5 are oriented in the same
relative relationship as the turbine sections 44, 46 in FIG. 3 with
respect to the directions of steam flow and the direction of rotor
expansion.
FIG. 4 illustrates portions of the high pressure casing 92 and a
stationary radial nozzle 102 in the steam turbine diaphragm
exhausting high pressure, low specific volume steam to a rotating
turbine bucket 104 disposed on the rotor member 84 (FIG. 3). A
high-low labyrinth steam packing shown generally at 106 consists of
two stages of toothed steam packings 108, 110 forming close
clearances with a bucket tip shroud 112 connecting the tips of
steam turbine buckets 104. Each of the packings includes a stepped
diameter or interlocking packing which is highly effective in
restricting steam flow, but which accommodates only limited
relative axial movement between rotating and non-rotating
members.
Reference to FIG. 5 illustrates a turbine stage from the
intermediate pressure section in the hot steady state operating
condition. Shown is a portion of casing 98 supporting a number of
radial nozzle vanes 114 exhausting steam into turbine buckets 116
which are radially disposed on a rotating turbine wheel 118. A
labyrinth steam packing 120 is provided by a single diameter
multi-tooth packing member 122 forming close clearances with a
circumferential shroud 124 connecting the tips of turbine buckets
116. Packing 120 is a single diameter packing which has
non-interlocking teeth and hence can accommodate substantial
relative movement between the rotating and non-rotating members.
Shown in phantom lines in FIG. 5 is the turbine wheel 118' and
turbine bucket 116' in the cold condition.
Similar packings to the high-low or interlocking labyrinth packings
of FIG. 4 are utilized between the shaft and the bore or inner
diameter of the diaphragms of the high pressure section shown in
FIG. 4. Similarly, single diameter, non-interlocking packings
having straight or slanted teeth permitting substantial relative
expansion similar to those shown in FIG. 5 are used between the
diaphragm bore and the rotor shaft of the lower pressure turbine
section. These packings are not shown but are similar to those
shown in FIGS. 4 and 5.
It remains to note that the two steam turbine casing members shown
in FIG. 3 are supported from the standards to permit independent
axial expansion of the casings from their foundation anchor points
in the following manner. The two steam turbine casings are each
affixed to the foundation fixed standard 60 at one end and expand
thermally independently of each other. The first or high pressure
casing 92 is rigidly keyed to the fixed standard at 61 on a pair of
support arms 93 on its inlet end, so that the casing and rotor both
expand to the right in the same direction away from the thrust
bearing 26. This is accommodated by sliding of an opposite pair of
casing support arms 95.
The inlet end 100 of the intermediate pressure casing 98 is
supported on a pair of support arms 99 keyed to the standard 76 as
indicated at 101. While the outlet end of casing 98 is supported
and axially restrained by the exhaust hood at key 58, standard 76
may deflect to the right on flexible legs 77. The inlet end of the
casing 98 grows in the same direction as the rotor expansion as
temperature increases. However, the total movement of the rotor
blades is greater than that of the casing in the intermediate
pressure turbine section, because the shaft system expands from the
thrust bearing 26 which is farther away than the point 58 where the
exhaust hood is keyed to the foundation. Therefore, a large
differential thermal expansion between rotating and non-rotating
members takes place at the inlet end of the lower pressure turbine
section. This large relative movement is illustrated in FIG. 5,
wherein it is seen that the rotor wheel 118 and turbine buckets 116
move closer to the nozzles 114 as the rotor expands to the hot
steady-state condition. This movement is permitted by use of single
diameter or non-interlocking multi-tooth packings.
Although the preferred location for the single thrust bearing 26 is
in the gas turbine compressor inlet standard, it can also be
located in the front bearing standard 60. In either case, the
thrust bearing is on the side of the steam turbine toward the gas
turbine. The preferred arrangement has the inlet end of the high
pressure casing of the reheat steam turbine where steam density is
the greatest, keyed to the foundation adjacent the location where
the thrust bearing is keyed to the foundation, where differential
expansion between stationary and rotating components is the least.
This arrangement minimizes efficiency loss due to steam leakage
flow.
MODIFICATION
A modified form of the invention is utilized in a combined cycle
illustrated schematically in FIGS. 7 and 8. In the modification,
the low pressure steam turbine sections are of the double-flow
configuration and the high pressure and intermediate turbine
sections are combined in a single opposed-flow casing. In order to
appreciate the difference between the invention and a conventional
reheat steam turbine, it is necessary to briefly discuss a prior
art arrangement shown in FIG. 6.
FIG. 6 illustrates a conventional two-casing reheat steam turbine
with a double flow low pressure section. As in the prior art single
flow unit shown in FIG. 1, the casings are both keyed to the
foundation at only one location at the center of the exhaust hood
outlet where the exhaust hood connects to the condenser, and the
thrust bearing is supported in a sliding standard to allow it to
move along with the casings. The steam PG,20 turbine includes a
first casing 51 which combines a high pressure section 52 and an
intermediate pressure section 53, and a second casing 55 containing
double flow low pressure turbine sections 59 supported within an
exhaust hood discharging to the condenser. The turbine rotors are
rigidly coupled to the rotor of a generator 63, and the single
shaft system and turbine casings are supported on bearing standards
79, 80 and 81. The low pressure casing 55 and exhaust hood are
keyed to the foundation at 89. The combined high pressure and
intermediate pressure casing is supported on arms keyed at 89 and
90 to bearing standards 79, 80, respectively. The single shaft
system is restrained axially by a thrust bearing 91 located in
bearing standard 79. Bearing standard 80 may move axially by
sliding on the foundation as indicated by arrows 63. The bearing
standard 79 with the thrust bearing is supported on flexible legs
43 and may also move axially as indicated by arrows 47. An
expansion bellows 97 in the crossover between casings 51 and 55
allows for differential thermal expansion between them.
In operation, the casings may grow thermally from foundation key 89
causing standards 79, 80, 81 to move axially. The shaft system is
located by the thrust bearing 91 in standard 79 adjacent the high
pressure section 52, where steam density is the greatest and where
differential expansion is the least, thus minimizing efficiency
loss due to steam leakage flow.
Referring now to the modification shown in FIG. 7 for a combined
cycle, a gas turbine shown generally at 126, reheat steam turbine
128 and generator 130 are disposed on a single shaft system 132 as
before comprising rigidly coupled rotor members and having a single
thrust bearing 134 disposed in the gas turbine compressor bearing
standard. The elements of the gas turbine 126 and generator 130 are
as previously described. However, the steam turbine 128 comprises a
high pressure turbine section 136 with an intermediate pressure
turbine section 138 receiving reheated steam from the reheater, but
arranged in a common or first casing 139 with the high pressure
turbine section 136. The intermediate pressure turbine 138 exhausts
steam through a crossover conduit 140 to a double-flow low pressure
casing 142. The crossover conduit 140 is arranged in a known manner
with expansion bellows 141 to permit relative movement between the
two casings 139 and 142.
Referring to FIG. 8, the details of reheat double-flow steam
turbine 128 are shown. A foundation which includes portions shown
at 144, 146, 148 supports the steam turbine 128. A bearing standard
150 is supported by foundation portion 144 and keyed thereto to
restrain its movement at 152. A bearing standard 154 on flexible
legs 156 is supported on foundation portion 146 and may move
axially as shown by arrows 158. The first casing 139 containing the
high pressure turbine section 136 and intermediate pressure turbine
section 138 is supported at the high pressure end on a pair of arms
160 keyed to the bearing standard at 162. The intermediate pressure
end is supported on a pair of arms 164 keyed to the axially movable
bearing standard 154 at 166.
The second casing comprising opposed flow low pressure turbine
sections 168, 170 are arranged in an exhaust hood 172 supported on
bearing standards 174, 176. The hood is keyed to the foundation at
178, and the ends are free to expand in both axial directions on
bearing standards 174, 176, which slide on foundation portions 146,
148.
FIG. 9 is a partial schematic view between casings 139 and 142,
showing an alternate arrangement, which permits independent axial
movement of both casings. A common bearing standard 180 is slidable
on foundation portion 182 as indicated by arrows 184 to allow the
casing 142 to move. Casing 139 is supported at one end on a pair of
arms 186 which may slide as indicated by arrows 188. Thus, as the
steam turbine casings heat up, casing 142 may move to the left on
the foundation, from its keying location 178, while casing 139 may
move to the right on the bearing standard from its keying location
152 adjacent the thrust bearing 134 (see FIG. 8).
As in the preferred arrangement, discussed previously in connection
with FIGS. 1-5, the double-flow modification discussed in FIGS. 6-9
locates the high pressure turbine section in the first casing on
the side of the steam turbine toward the gas turbine where the
thrust bearing is keyed to the foundation, so that differential
thermal expansion between the high pressure turbine casing and its
rotor is minimized. Also, as before, the intermediate pressure
turbine casing is supported on a bearing standard which allows it
to move axially with respect to the foundation. Also, as before,
the exhaust hood is keyed to the foundation near the center of its
opening to the condenser and and expands thermally away from the
central points where it is keyed to the foundation. The single
shaft system expands through the entire steam turbine stationary
portion. However, the units are arranged such that relative thermal
expansion is minimized at the high pressure end and permitted on
the low pressure end where it is less critical in its effect on
efficiency.
In summary, the improved two-casing reheat steam turbine of the
present invention employs a novel combination of casing arrangement
and keyed points to permit it to be solidly coupled to a gas
turbine and generator on a shaft having a single thrust bearing and
having the generator on one end of the equipment train. The
mechanical requirements for all rotating and stationary components
to expand and contract freely, for maintaining a stationary point
of connection of the exhaust hood to the condensor and for the
balancing of thrust load through use of opposed sections are met.
The novel combination of casing arrangement and anchor points
permits the large differential expansion while achieving close
axial spacing of the stationary nozzles and rotating buckets in the
hot operating condition in the high pressure and intermediate
pressure turbine sections. Therefore, with the present invention, a
single shaft combined cycle machine can be built which has
essentially the same level of efficiency as a more complex and
expensive plant having gas turbine and steam turbine generators on
separate shaft systems.
* * * * *